1. Field of the Invention
The present invention relates to a grain-oriented electrical steel sheet used for the iron core of a transformer, etc. and, more specifically, to a low iron loss and low noise grain-oriented electrical steel sheet contributing to lowering not only the iron loss but also the noise of an iron core, and a method for producing the same.
2. Description of the Related Art
In recent years, it has been desired to reduce the noise and vibration of devices, in which electromagnetism is applied, such as transformers, and it has increasingly been required that a grain-oriented electrical steel sheet used for the iron core of a transformer is a material having not only low iron loss but also low noise and low vibration. It is said that magnetostriction of a grain-oriented electrical steel sheet is one of the causes for the noise and vibration of a transformer. Magnetostriction, as cited here, means the vibration generated in the rolling direction of the steel sheet when a grain-oriented electrical steel sheet is magnetized by alternating current, and the magnitude is as small as about 10−6. However, it has not been clarified what kinds of magnetostriction properties are effective for lowering the noise of a transformer.
The measure to lower noise has so far been to reduce magnetostriction. It is known that magnetostriction can be lowered by increasing the integration degree in the orientation of {110}<001> of secondary recrystallization grains. This is the same common measure as employed when iron loss reduction is required. As one of the proposals for materials in which magnetostriction is positively lowered, Japanese Unexamined Patent Publication No. H8-269562 is disclosed. In this publication, it is attempted to lower magnetostriction by intentionally leaving internal residual strains at annealing. However, by this method, hysteresis loss increases, causing an increase in iron loss, since the strains remain.
As mentioned above, the magnetostriction properties of a material for an iron core designed to lower the noise of a transformer have not clearly been proposed so far, and also those of a material to lower magnetostriction vibration have scarcely been proposed.